This invention relates to apparatus and the method of detecting failure of a defrost system for refrigerating apparatus.
Automatic defrosting systems for refrigerating apparatus have been utilized for a long time wherein periodically some form of heat usually from an electric resistance heater is utilized to remove accumulated frost buildup on the refrigerating apparatus evaporator. The normal operation of refrigerating apparatus would include some kind of timer device which would operate to provide the refrigerating mode operation for a period of time and then terminate the refrigerating mode and initiate a defrosting mode wherein the electric resistance heater is energized causing it to heat up and radiate heat to the evaporator for a period of time sufficient to melt the built-up frost on the evaporator. When the frost has been removed from the evaporator, a defrost terminating thermostat in thermal relationship with the evaporator senses a rise in temperature and at some predetermined elevated temperature opens to terminate the defrost operation. An example of such an automatic defrost system is disclosed in U.S. Pat. No. 3,394,55l9 and also in U.S. Pat. No. 4,156,350 both of which are assigned to the same assignee as the present invention.
In the event that the defrost system becomes inoperative, the result is accumulated buildup of frost on the evaporator to such an extent that poor cooling performance of the refrigerating system results. It is desirable in refrigerating apparatus having automatic defrost systems that should there be a failure of the defrost system that there be some kind of early alarm signal to alert the user that the defrost system is inoperative and should be repaired.
Detection of failure in electrical circuits by having indicator lights come on when there is a break in the circuit has been known for years and such signal arrangements are shown in U.S. Pat. Nos. 1,730,366 and 3,147,466. These signal arrangements, however, provide for a signal only when there is a break in the circuit. In present refrigerator defrost systems, there is an intentional break in the circuit provided when the defrost terminating thermostat switch opens to deenergize the heater and stop the defrosting mode. There is, therefore, a need for providing failure detection in a refrigerating apparatus defrost system wherein a break in the circuit does intentionally occur periodically, however, an alarm signal would only be actuated when there is an unintentional break in the circuit that persists over a relatively long period of time.